The R value of extruded polystyrene is roughly R5 per inch. It has excellent value, but uncovered is unfinished. The contractor had no business leaving it that way.

Tom, I always thought so too, but we have a good friend who is a dry wall installer and he says most of the homes he does have unfaced batts in them with no vapor barrier. So I am confused. Mightyanvil, the exterior walls are 2x6 with OSB sheathing, house wrap and vinyl siding. The ceilings are vaulted in most of the house. the HVAC is a little undersized, but we will suppliment with wood heat. Hopefully the AC will be enough...it was a gas pac we already had so we are using it. The northern exposure of the house has an attached sunroom that runs almost the entire length of the house, so we will be a lot of protection from the north winds. Humidity here...well, it is pretty high in the summer but not like the gulf coast or anywhere like that. so....give that info, what do you think? I do trust this insulator...he has been doing this for a long, long time in this area.

We considered all types of insulation for our victorian rehab and finally settled on foam because of the aforementioned wall depth. There are several types of foam, the one we chose is supposedly "green" - SPF. To achieve the same R-value with fiberglass would have meant losing 2" on each exterior wall, which we could not do. Denim would be great but it was just too pricey and given the scope of our renovation, couldn't be worked into the budget. Some info on SPF...from their literature: SPF is environmentally friendly, contains no formaldehyde or ozone depleting chemicals, saves energy* and reduces the use of fossil fuels, thereby reducing global warming gases. It also assists in providing good indoor air quality, requires less energy to produce than the leading insulation, and reduces the amount of energy required to transport and install it. SPF is durable, maintains physical properties over time, contributes little to the waste stream, and in a single product (depending on the formula and project) can take the place of three-four other products, including insulation, air barriers, sealants, vapor retarders, and weather barriers. *SPF reduces energy use in the following ways: Has high R-value per inch Eliminates air infiltration Helps control moisture and condensation Reduces convective currents in walls and attics Eliminates wind washing Effective at low and high temperatures Provides the correct environment so that the ventilation system performs more efficiently Other benefits include... Closed cell SPF adds structural strength and glues a building together, thereby making it more resistant to racking events, such as hurricanes and high winds. SPF reduces noise from outside by air sealing the building. Closed-cell SPF can provide an added barrier against water intrusion. COMFORT: SPF reduces drafts and increases comfort. SPF helps maintain a comfortable, constant, temperature throughout the building, from room to room and floor to floor. HEALTH: SPF assists in improving indoor air quality. SPF reduces the infiltration of outside air pollutants and soil gases. SPF can reduce moisture condensation and mold growth within the building walls and roof. VALUE: Excellent insulation efficiency of SPF can reduce heating and cooling usage dramatically. HVAC equipment can be down-sized, thereby reducing construction costs. SPF will not sag or settle. SPF can eliminate the need for separate housewrap and vapor retarders. ENVIRONMENT: SPF helps conserve energy, reducing CO2 emissions. SPF contributes LEED credits for sustainable, green construction. SPF can help reduce structural damage caused by high winds. SPF contains no formaldehyde or ozone depleting substances.

By leaving a gap, you are creating an unconditioned space between the insulation and the foundation wall where moisture will form from condensation, creating perfect conditions for mould growth. As well, the convection loops facilitated by the open space will eliminate the insulating effect of the insulation. Indeed, even gaps as thin as a line of glue on insulating panels can result in circulating air. See the below excerpt from Jon Eakes, citing Canada Mortgage and Housing Corporation research.